In recent years, circulatory system diseases caused by arterial sclerosis are increasing, and an evaluation device for evaluating a degree of arterial sclerosis of a blood vessel is accordingly being put to practical use. A pulse wave velocity method is known as a typical method of evaluating the degree of arterial sclerosis. The pulse wave velocity method uses a correlation between a velocity (pulse wave velocity) at which change in blood pressure involved in beating of a heart is propagated through the blood vessel and a degree of elastic force (rigidity) of the blood vessel. In other words, as a pulse wave advances through the blood vessel, which is an elastic tube, the pulse wave velocity increases the harder the tube wall, the narrower the inner diameter, and the thicker the tube thickness, and thus the degree of arterial sclerosis can be known by measuring the pulse wave velocity. In particular, an evaluation device by a baPWV method (brachial-ankle Pulse Wave Velocity method) using the time waveform of blood pressure at both upper arms and both angles is being put to practical use.
As a measurement method of the pulse wave velocity, Japanese Unexamined Patent Publication No. 2006-326334 (Patent Document 1) discloses a pulse wave propagation velocity measurement device including detection means for detecting a temporal distortion between voltage waveforms obtained from adjacent voltage electrode pairs out of a plurality of voltage waveforms, and calculating means for obtaining a rate of change of the pulse wave propagation velocity or the pulse wave propagation time between the adjacent voltage electrodes using a distance between the adjacent voltage electrodes and/or a temporal shift for all of the plurality of voltage waveforms.    Patent Document 1: Japanese Unexamined Patent Publication No. 2006-326334